Interstitial pulmonary fibrosis is characterized by alterations in the lung parenchyma with excess connective tissue, increased rate of collagen synthesis and altered type I:III collagen ratio. Fibroblasts are believed to be the major cell type responsible for the production of excess connective tissue constituents. We and others have previously shown that fibroblasts are heterogeneous, that not all fibroblasts respond alike to environmental mediators, and that fibroblast populations can be separated based on specific interactions between fibroblast subpopulations and substances released by inflammatory cells lead to cell selection, and that presence of fibroblast subpopulations with distinctive properties contribute to the evolution and genesis of fibrosis. We propose to isolate fibroblasts from adult, normal human lungs and from lungs with early and late fibrosis, and to characterize their growth characteristics, production of collagen and elastin, contractile properties, and C1q binding. We will separate fibroblast subpopulations from cultures of normal lungs using a fluorescence-activated cell sorter based on differences in C1q binding, and determine their properties. We will then sort fibrotic lung fibroblast cultures and examine the populations obtained. We will determine whether the fibroblast subpopulations obtained in this manner differ in their response to three inflammatory mediators known to be involved in fibroblast regulation: PDGF, TGF-beta, and gamma-interferon. Finally, we propose to identify specific phenotypic markers for fibroblast subpopulations and develop probes to identify these cells. We will generate cDNA libraries using mRNA isolated from parent cultures, hybridize them with labeled cDNA from fibroblast subpopulations, and identify clones containing specific DNA sequences. We will also attempt to utilize a battery of antibodies to differentiate fibroblast subsets. Using these probes, we propose to identify fibroblast subpopulations in normal and fibrotic lung tissue specimens. We expect that from these results we will be able to determine how fibroblast subpopulations contribute to pulmonary fibrosis.